With PD4ML Pro you may do that by inline footer definition:
<pd4ml:page.footer>
<b>All rights reserved. Powered by PD4ML</b>
</pd4ml:page.footer>
With PD4ML Std it could be done via API call. See more about footers/header:
html-pdf-faq-f1/pdf-page-headers-footers-definition-options-t41.html